#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define endl '\n'
const int N = 2e5 + 5;

int n, m;
string s;

int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> s;
  int cnt = 0;
  for (char c : s) cnt += c - '0';
  cout << cnt;
  return 0;
}